POSSIBLE SPECIES

Plesiosaur

In 1933 it was suggested that the creature "bears a striking resemblance to the supposedly extinct plesiosaur," a long-necked aquatic reptile which became extinct during the Cretaceous-Paleogene extinction event. A popular explanation at the time, the following arguments have been made against it:

Plesiosaurs were probably cold-blooded reptiles needing warm tropical waters; the average temperature of Loch Ness is only about 5.5°C (42°F). If the plesiosaurs were warm-blooded, they would require a food supply beyond that supplied by Loch Ness.

In an October 2006 New Scientist article, "Why the Loch Ness Monster is no plesiosaur," Leslie Noe of the Sedgwick Museum in Cambridge said: "The osteology of the neck makes it absolutely certain that the plesiosaur could not lift its head up swan-like out of the water."

The loch is only about 10,000 years old, dating to the end of the last ice age. Before then, it was frozen for about 20,000 years.

If creatures similar to plesiosaurs lived in Loch Ness they would be seen frequently, since they would have to surface several times a day to breathe.

In response to these criticisms, Tim Dinsdale, Peter Scott and Roy Mackal postulate a trapped marine creature which evolved from a plesiosaur directly or by convergent evolution. Robert Rines explained that the "horns" in some sightings as breathing tubes (or nostrils), allowing it to breathe without breaking the surface.

Long-necked giant amphibian

R. T. Gould suggested a long-necked newt; Roy Mackal examined the possibility, giving it the highest score (88 percent) on his list of possible candidates.

Invertebrate

In 1968 F. W. (Ted) Holiday proposed that Nessie and other lake monsters, such as Morag, may be a large invertebrate such as a bristleworm; he cited the extinct Tullimonstrum as an example of the shape. According to Holiday, this explains the land sightings and the variable back shape; he likened it to the medieval description of dragons as "worms."" Although this theory was considered by Mackal, he found it less convincing than eels, amphibians or plesiosaurs.